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The Weather of January 2011

     Due to the frequent replenishments of the winter monsoon, the monthly mean temperature of 13.7 degrees for the first month of 2011 was 2.4 degrees below normal, making it the coldest January since 1977.  There were 14 cold days (daily minimum temperature at 12 degrees or below) in the month, doubling the normal figure of 7 days.  The temperature did not rise to 20 degrees or above for the month which only occurred once in 1918 for January on record.  The month was also drier than usual with only 5.4 millimetres of rainfall, about 22 percent of the normal figure.

     Under the influence of a dry northeast monsoon, the weather was fine and dry for the first day of the month.  A strong easterly airstream affected the coastal areas of Guangdong and brought windy and cloudy weather to Hong Kong on 2 January.  It remained cloudy with some light rain patches for the ensuing three days.  With the arrival of an intense winter monsoon on 6 January, a cold spell began to affect Hong Kong lasting until 13 January. There were light rain patches on 6 and 7 January.  Affected by a dry northerly airstream, the weather turned fine and dry but remaining cold in the morning from 8 to 10 January.  An extensive cloud band over southeastern China brought some rain to the territory from 11 to 13 January.  The temperature fell to a minimum of 7.2 degrees at the Hong Kong Observatory on the morning of 12 January, the lowest of the month. 

     With the moderation of the winter monsoon and abundant sunshine, the weather turned mild in Hong Kong on 14 January.  The temperature at the Hong Kong Observatory rose to a maximum of 19.4 degrees, the highest of the month.  Cold and windy weather resumed the next day when another surge of the winter monsoon reached the south China coast.  It remained cold and dry on 16 and 17 January. 

     The local weather was mainly fine on 18 and 19 January.  It turned cloudy with some haze on 20 January.  With a replenishment of the winter monsoon, it became cold again in the morning with fine and dry weather on the next day.  It remained generally fine with some haze from 22 to 28 January.  Another replenishment of the winter monsoon reached the south China coast later on 28 January, bringing cold and dry weather to Hong Kong for the last three days of the month.

    There was no tropical cyclone over the South China Sea and the western North Pacific in the month.

     Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4.  Monthly meteorological figures and departures from normal for January are tabulated in Table 2.

Warnings and Signals issued in January 2011


Table 1.1   Strong Monsoon Signal

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
2 / 1 0005 2 / 1 0950
15 / 1 0730 16 / 1 0445
21 / 1 0915 21 / 1 1130
29 / 1 0305 29 / 1 1145


Table 1.2   Fire Danger Warnings

Colour Beginning Time Ending Time
Day/Month HKT Day/Month HKT
Red 28 / 12 0630 1 / 1 2355
Yellow 1 / 1 2355 3 / 1 1055
Yellow 7 / 1 0000 9 / 1 0600
Red 9 / 1 0600 11 / 1 0645
Yellow 14 / 1 0600 15 / 1 0600
Red 15 / 1 0600 16 / 1 2245
Red 17 / 1 0600 17 / 1 2045
Red 21 / 1 0600 22 / 1 0600
Yellow 22 / 1 0600 23 / 1 2000
Yellow 24 / 1 0600 25 / 1 0745
Yellow 26 / 1 1130 26 / 1 1800
Red 28 / 1 2245 31 / 1 2200


Table 1.3   Frost Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
11 / 1 1630 12 / 1 0745
15 / 1 1630 16 / 1 1015
17 / 1 0350 17 / 1 0945


Table 1.4   Cold Weather Warning

Beginning Time Ending Time
Day/Month HKT Day/Month HKT
30 / 12 1620 2 / 1 0745
3 / 1 1620 14 / 1 0600
14 / 1 1620 25 / 1 1145
28 / 1 1620 3 / 2 0945


Table 2   Figures and Departures from Normal - January 2011

Meteorological Element Figure of the Month Departure from Normal*
Mean Daily Maximum Air Temperature 16.3 degrees C 2.3 degrees below normal
Mean Air Temperature 13.7 degrees C 2.4 degrees below normal
Mean Daily Minimum Air Temperature 11.6 degrees C 2.5 degrees below normal
Mean Dew Point Temperature 7.5 degrees C 3.5 degrees below normal
Mean Relative Humidity 67 % 6 % below normal
Mean Cloud Amount 63 % 3 % above normal
Total Rainfall 5.4 mm 19.5 mm below normal
Number of hours of Reduced VisibilityΔ 376 hours 137.1 hours above normal§
Total Bright Sunshine Duration 158.6 hours 16.9 hours above normal
Mean Daily Global Solar Radiation 11.38 Megajoule / square metre 0.83 Megajoule above normal
Total Evaporation 84.1 mm 3.4 mm above normal


  Remarks : All measurements were made at the Hong Kong Observatory except sunshine, solar radiation and evaporation which were recorded at King's Park Meteorological Station and visibility which was observed at the Hong Kong International Airport.
  Δ

The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.


  *   Departure from 1971 - 2000 climatological normal, except for number of hours of reduced visibility

  §   Departure from mean value between 1997 and 2010

daily values of selected meteorological elements for HK for January 2011

Extract of Meteorological Observations in Hong Kong for January 2011